This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Tail-anchored (TA) proteins represent a unique family of transmembrane proteins which contain a single transmembrane helix (about 25 residues) at the C-terminus. The mechanisms how the TA proteins insert the TMD into membranes are distinct from the well-studied co-translational insertion pathway, which is mediated by the cytosolic signal recognition particle (SRP). The post-translational insertion of the TA proteins into ER membrane requires the Golgi ER trafficking (GET) complex which contains Get1, Get2 and Get3. Get3 is an ATPase and can recognize and bind the C- terminal transmembrane domain (TMD) of the TA proteins. It is not well understood how GET complex accomplish the membrane insertion of the TA protein. Recently we have determined the yeast Get3 crystal structure in the open conformation. The structure suggested that Get3 may adopt an open conformation in nucleotide-free state and a closed conformation in ATP-bound state. The conformational changes to switch the Get3 between the open and closed conformations may facilitate the membrane insertions for TA proteins. Get3 may share a similar mechanism as the ABC transporters to transfer bound ligands. Now we are requesting beam time to determine Get3 crystal structure in the closed conformation to confirm our hypothesis.